Genetic Mutation Caused Nonhereditary White Coat Color Pattern

Researchers recently discovered a new genetic mutation in a Thoroughbred foal that was born with large portions of nonpigmented skin. Whether another horse with the same rare mutation will be born is unknown, but the discovery has fueled researchers' pursuit of knowledge about coat color-related genetics and its potential relationship to serious health problems or death.

Essential to skin pigment is the function of a particular multipurpose gene, called KIT (an acronym for the actual genes involved), which the researchers examined in the current study. The KIT gene specifies the genetic code for a special protein called a tyrosine kinase receptor, expression of which is essential for the proper development of a variety of cell types, including red blood cells, mast cells of the immune system, and melanocytes (pigment-producing cells located in the bottom layer of the skin).

"KIT mutations cause abnormal melanocytes that do not produce pigment in the skin," explained Heather Holl, BSc, a PhD student in the Department of Animal Science at Cornell University. "The result is horses with pink skin and white hair. The amount of affected skin varies and ranges from small patches of depigmentation to white over the entire body."

To date, researchers have identified 14 different mutations involving the equine KIT gene, including the Sabino-1 and Tobiano color patterns.

Holl explained, "We suspected a new mutation after the birth of a Thoroughbred colt with extensive white markings. Both the parents had only small white markings and the sire had over 400 registered offspring without a single recorded dominant white foal."

Holl, together with Samantha A. Brooks, PhD, an assistant professor in the same department at Cornell, and Ernest Bailey, PhD, from the University of Kentucky's Gluck Equine Research Center, subsequently analyzed the DNA sequence of parts of the foal's KIT gene and found a novel deletion in the gene that involved just five base pairs of DNA out of the 2.7 million base pairs present in the equine genome.

"Neither parent had the mutation," Holl added.

The colt died unexpectedly at five weeks of age. It remains to be determined if the KIT mutation played a role in his death.

"Unfortunately, there is not much else we can do with this (case)," concluded Holl. "From the data we have, we cannot confirm the mutation was involved in the foal's death, and it is unlikely that another will be born like him; however, we (continue to) work with other white patterns in the horse, including other suspected dominant white cases."

Dominant white cases are uncommon. When a horse has one dominant white gene, the result will be a pure white horse that lacks pigment in the skin from birth, so they are easy to detect. However, a previous study of dominant white horses showed that breeding white horses to white horses can cause embryonic losses.

The study, "De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern," was published in a special edition of Animal Genetics. The entire journal supplement, funded by the Dorothy Russell Havemeyer Foundation is available for free online.

About the Author

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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